Project Summary This application proposes a dyadic experiment to investigate the role of social support in tempering stress reactivity in older adulthood. Close relationship partners, especially one's romantic partner, are essential to physical and mental health during all life stages and become especially important in older adulthood. Models of lifespan development have proposed that relationship partners in older adulthood are vital because they help people adapt to age-related declines. Among these declines is exacerbated physiological reactivity to stress. This stress reactivity poses significant threats to older adults' health. Yet, relatively little work has investigated how relationship partners might protect against these negative effects. Social support?emotional and practical assistance from close others?may be a key mechanism through which relationships partners help older adults compensate for this increased stress reactivity. Despite the potential importance of social support in older adulthood, prior work has been limited due to: (1) a lack of studies using dyadic paradigms to examine support discussions between partners dynamically as they unfold; and (2) a lack of experimental studies to test potential causal effects of social support receipt. Therefore, further research is urgently needed to reveal the implications of social support for attenuating stress reactivity in older adulthood and to build a foundation for developing relationships-based interventions to promote healthy aging. To narrow these gaps, this proposal will use a dyadic experiment to investigate individual self-regulatory effects (Aim 1) and dyadic coregulatory effects (Aim 2) of social support in older adulthood and to model the between-person heterogeneity of these effects (Aim 3). Romantic partner dyads ages 65+ will participate in a laboratory experiment together. One partner (?target?) will be asked to give a speech, a stressor commonly used in stress paradigms with older adults. Dyads will then be randomly assigned to engage in a social support discussion or control discussion in anticipation of the stressor. To examine affective regulation, we will measure participants' self-reported mood and perform observational coding of participants' expressions of positive and negative emotion during the discussion and stressor. To examine physiological regulation, blood pressure and heart rate variability will be monitored continuously during the discussion and stressor. Analyses will be performed using dynamical systems modeling, a focus of the proposed training plan, to gauge the degree to which social support tempers affective and physiological stress reactivity at the individual and dyadic levels of analysis. This work will be among the first to use dyadic experimental methods to investigate how social support protects older adults from the harmful effects of stress and will directly address NIA's goal of understanding how relationships enable healthy aging. Completion of this project will be supported by a predoctoral training plan focused on aging/lifespan development, advanced statistical methods, social psychology, and professional development.